It is desirable for some types of communication performed between devices on a network to establish a session before starting the communication. Such a type of communication for which an advance session establishment is desirable is, e.g., telnet for remote control of another device on the network. The term session means a process between a start and an end of a logical connection in the communication performed on the network.
Technologies of session management for using sessions effectively are known, as the number of sessions simultaneously established among devices on the network is limited. One of such technologies is, e.g., to close unused one of established sessions so as to use sessions of a limited number effectively.
Another one of such technologies is to close sessions except for an emergency call made in a case where the number of established sessions has reached the upper limit, and to establish a new session to be allotted to the emergency call. Still another one of such technologies is to watch duration of each of established sessions and to close a session whose duration is over a particular period of time so as to use sessions of a limited number effectively.
Yet another one of such technologies is, in a case where a device that a session is to be established with conceivably demands a longer period of time than a particular time length for making a reply in communication, to limit a session to be established with that device so as to use sessions of a limited number effectively. Further, a technology related to a communication device is to close a session in use according to a timeout condition in an http (Hypertext transfer Protocol) protocol so as to use sessions of a limited number effectively. Another technology related to a communication device is to send a heartbeat message and to maintain a session having been established with that communication device in order to keep the session in use from being closed according to a timeout condition.
Japanese Laid-open Patent Publications Nos. 2005-244964, 2009-219076, 2009-217445, 2005-184165 and 2006-20301 discuss the related art.